Method and device for controlling an irradiation system for producing workpieces

ABSTRACT

The invention relates to a method for controlling an irradiation system (20), the irradiation system (20) being used in a device (10) for the additive manufacturing of three-dimensional workpieces and comprising at least three irradiation units (22a-d, 50), the method comprising the following steps: a) defining an irradiation region (30a-d) for each of the irradiation units (22a-d, 50), the irradiation regions (30a-d) each comprising a portion of an irradiation plane (28) which extends parallel to a carrier (16) of the device (10), and the irradiation regions (30a-d) being defined such that they overlap in a common overlap region (34); b) irradiating a raw material powder layer on the carrier (16) to produce a workpiece layer; c) arranging a further raw material powder layer on the already jetted raw material powder layer to produce a further workpiece layer. d) The invention also relates to a device for performing this method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase of international applicationPCT/EP2018/050843, filed on Jan. 15, 2018, which claims the benefit ofGerman application DE 10 2017 202 843.2 filed on Feb. 22, 2017; all ofwhich are hereby incorporated herein in their entirety by reference.

The invention relates to a device and a method for controlling anirradiation system, wherein the irradiation system is used for theadditive manufacture of three-dimensional workpieces. The irradiationsystem comprises at least three irradiation units with mutuallyoverlapping irradiation regions.

In additive methods for the manufacture of three-dimensional workpieces,and in particular in additive layer building methods, it is known tosolidify an initially shapeless or shape-neutral molding compound (forexample a raw material powder) by location-specific irradiation andthereby bring it into a desired shape. Irradiation can take place bymeans of electromagnetic radiation, for example in the form of laserradiation. In a starting state, the molding compound can initially be inthe form of granules, powder or a liquid molding compound and can beselectively or, in other words, location-specifically solidified as aresult of the irradiation. The molding compound can comprise, forexample, ceramics, metal or plastics materials and also materialmixtures thereof. A variant of additive layer building methods relatesto so-called powder bed fusion, in which in particular metallic and/orceramics raw material powder materials are solidified to formthree-dimensional workpieces.

In order to produce individual workpiece layers it is further known toapply raw material powder material in the form of a raw material powderlayer to a carrier and to irradiate it selectively and in accordancewith the geometry of the workpiece layer that is currently to beproduced. The laser radiation penetrates the raw material powdermaterial and solidifies it, for example as a result of heating, whichcauses fusion or sintering. Once a workpiece layer has solidified, a newlayer of unprocessed raw material powder material is applied to theworkpiece layer which has already been produced. Known coaterarrangements can be used for this purpose. Irradiation is then againcarried out on the raw material powder layer which is now uppermost andis as yet unprocessed. Consequently, the workpiece is gradually built uplayer by layer, each layer defining a cross-sectional area and/or acontour of the workpiece. It is further known in this connection to useCAD or comparable workpiece data in order to manufacture the workpiecessubstantially automatically.

Solutions are also known in which the irradiation of the raw materialpowder material is carried out by an irradiation system which comprisesa plurality of irradiation units. These are able to irradiate a singleraw material powder layer together and thereby act in parallel or offsetrelative to one another in terms of time.

It will be appreciated that all of the aspects discussed above canlikewise be provided within the context of the present invention.

An example of a solution in which a plurality of irradiation unitstogether irradiate a single raw material powder layer is to be found inEP 2 875 897 A1. There are disclosed therein two irradiation units whoseirradiation regions overlap in a common overlap region. A workpiecelayer to be produced is first evaluated to determine which portions ofthe workpiece layer that are to be produced extend into the irradiationregions of the individual irradiation units and which portion extendsinto the common overlap region. These portions to be produced are thenassigned to the respective irradiation units, wherein the portion in thecommon overlap region that is to be produced can be additionallysubdivided.

The use of different irradiation units for jointly irradiating a rawmaterial powder layer, which is synonymous with the joint production ofa workpiece layer by different irradiation units, can lead to ashortening of the manufacturing time compared with the use of only oneirradiation unit.

The inventors have, however, recognized that irradiation by means ofdifferent irradiation units can lead to inhomogeneities of themanufactured workpiece. This can relate especially to the workpiecestructure and result in substantial quality defects of the manufacturedworkpiece.

Accordingly, the object of the present invention is to provide a deviceand a method for the additive manufacture of three-dimensionalworkpieces which permit a comparatively short manufacturing time with ahigh workpiece quality.

To that end there is provided a method for controlling an irradiationsystem, wherein the irradiation system is used in a device for theadditive manufacture of three-dimensional workpieces and comprises atleast three irradiation units. The device can be configured tomanufacture the three-dimensional workpiece in the manner of selectivelaser sintering. The irradiation units can be configured to emit anelectromagnetic processing beam, for example in the form of a laserbeam. To that end they can comprise suitable processing optics and/orradiation sources or can be capable of being connected to such units.According to one embodiment, at least two of the irradiation units areconnected to a common radiation source. The processing beam generated bythe radiation source can thereby be split and/or deflected by suitablemeans in order to be guided to the individual irradiation units. Therecome into consideration as suitable means for that purpose beamsplitters and/or mirrors.

The processing optics can guide at least one processing beam and/orinteract therewith in the desired manner. For this purpose they cancomprise objective lenses, in particular an f-theta lens.

The irradiation units can further comprise deflection devices fordirecting the emitted processing beams onto predetermined regions withinan irradiation plane and thus onto predetermined regions of a rawmaterial powder layer that is to be irradiated. The deflection devicescan comprise so-called scanner units, which are preferably adjustableabout at least two axes. In addition or alternatively, the irradiationunits, or at least the regions thereof that emit beams, can be movablein space. This can include in particular a movement relative to anirradiation plane, so that the irradiation units can be located oppositedifferent regions of the irradiation plane.

The method comprises the step a) of defining an irradiation region foreach of the irradiation units, wherein the irradiation regions eachcomprise a portion of an irradiation plane which extends parallel to acarrier of the device, and wherein the irradiation regions are sodefined that they overlap in a common overlap region.

The irradiation plane can be a two-dimensional planar plane. Theirradiation plane can in each case comprise a raw material powder layerthat is currently to be irradiated. Accordingly, its position relativeto the carrier can change depending on the raw material powder layerthat is to be irradiated. In particular, a distance from the carrier canincrease as the manufacturing time and number of layers of the workpieceadvance. The irradiation plane can further be arranged opposite thecarrier and preferably be congruent with a build area defined by thecarrier. The build area can be an area within which a workpiece can bemanufactured. More precisely, the build area can define a maximumcross-sectional area of the workpiece that can be manufactured.

The irradiation regions can comprise an areal portion of the irradiationplane, wherein those areal portions can also overlap. In other words, itis provided that all the irradiation regions overlap at least in thecommon overlap region or, in other words, that all the irradiationregions coincide in the overlap region. The overlap region can thusdefine an areal portion of the irradiation plane into which all theirradiation regions extend. In addition, further overlap regions canalso exist, in which only two of the irradiation regions overlap (in thefollowing also: secondary overlap region).

The definition of the irradiation regions can take place by specifyingthe deflection spectrum of the deflection units of the irradiation unitsand/or by specifying a possible movement spectrum of the irradiationunits. This can take place by defining suitable value ranges in acontrol unit of the device.

Outside the overlap region it can thus be provided that irradiation ofthe raw material powder layer within a particular irradiation regiontakes place only by means of the associated irradiation unit. Accordingto a variant it is provided that a first irradiation region isassociated with a first irradiation unit, a second irradiation region isassociated with a second irradiation unit and a third irradiation regionis associated with a third irradiation unit. Any further irradiationregion can be associated with any further irradiation units. The firstto third irradiation regions overlap in the overlap region. Outside theoverlap region, however, it is provided in this variant that theremaining portion of the first irradiation region can be irradiated onlyby the first irradiation unit, the remaining portion of the secondirradiation region can be irradiated only by the second irradiationunit, the remaining portion of the third irradiation region can beirradiated only by the third irradiation unit, and the remaining portionof any further irradiation regions can be irradiated only by theassociated further irradiation units.

The method further provides the step b) of irradiating a raw materialpowder layer arranged on the carrier in order to produce a workpiecelayer. The irradiation can take place via the irradiation units of theirradiation system, wherein, depending on the definition of theirradiation regions, they can irradiate different but, for example, inthe overlap region also common portions of the raw material powderlayer.

The carrier can be provided in a process chamber of the device. It canbe a generally fixed carrier or a displaceable carrier which isdisplaceable in particular in the vertical direction. According to avariant, the carrier is lowered in the vertical direction as the numberof workpiece layers produced increases and preferably in dependence onthat number. The process chamber can be capable of being sealed withrespect to the surrounding atmosphere in order to establish a controlledatmosphere, in particular an inert atmosphere, therein. The raw materialpowder layer can comprise all of the above-mentioned raw material powdermaterials and in particular a powder of a metal alloy. The powder canhave any suitable particle size or particle size distribution. Aparticle size of the powder of <100 μm is preferred.

The application of the raw material powder layer to the carrier and/orto a raw material powder layer arranged thereon and already irradiatedcan take place via known coater units or powder application device. Anexample thereof is to be found in EP 2 818 305 A1.

Within the context of the present disclosure, the term “workpiece layer”can relate generally to a workpiece layer to be produced from a singleraw material powder layer, that is to say in particular a cross-sectionthat is to be produced of the workpiece. The workpiece layer can furthercomprise a contour, for example in the form of an outer contour or of anoutline of the cross-section that is to be produced. In addition oralternatively, the workpiece layer can comprise an at least partiallyfilled area, for example in order to produce a filled or solidcross-sectional area of the workpiece. For this purpose there can beused a predetermined scan or irradiation pattern in which a plurality ofscan vectors are in known manner defined within the irradiation plane inorder to permit substantially extensive solidification.

For the irradiation, an analysis can be carried out beforehand todetermine which portions of the workpiece layer to be produced extendinto the individual irradiation regions and into the common overlapregion. Those portions outside the overlap region can be irradiated bythe irradiation units which are associated with the irradiation regionsin question. Within the overlap region, however, the plurality of theirradiation units are available for irradiation. Overall, the workpiecelayer to be produced can thus be composed of the portions irradiated byeach of the irradiation units. Further details of this procedure, whichrelate in particular to the splitting of a workpiece contour to beproduced and/or of a scan or irradiation pattern between differentirradiation units, are to be found in EP 2 875 897 A1 mentioned at thebeginning.

The method further provides the step c) of arranging a further rawmaterial powder layer on the already irradiated raw material powderlayer in order to produce a further workpiece layer. This can makepossible the described cyclic layer-by-layer manufacture of theworkpiece, in which new raw material powder layers are continuouslyapplied to already irradiated raw material powder layers, irradiated andsolidified location-specifically.

The method according to the invention is characterized first in that atleast three irradiation units are provided. In the common overlapregion, a plurality of irradiation units are thus available, from whicha flexible selection can be made.

According to the invention it can further be provided that theproportions of the irradiation regions in the irradiation plane are eachbetween 0% and up to and including 100%; and/or that the proportion ofthe overlap region in the irradiation plane is between 0% and up to andincluding 100%. In other words, it is also possible to providefull-field coverage, in which the irradiation regions each cover up toabout 100% of the irradiation plane. Consequently, each region of theirradiation plane can be irradiated by each of the irradiation units.Furthermore, the overlap region in this case likewise occupies aproportion of about 100% of the irradiation plane. Alternatively, it is,however, likewise conceivable that the overlap region and/or that theirradiation regions occupy not more than about 50% or not more thanabout 20% of the irradiation plane.

According to a further development, the irradiation units and/or thecenters of the respective irradiation regions span a polygon. In otherwords, it can be provided that the irradiation units and/or the centersof the respective irradiation regions do not lie on a common line. Forexample, the at least three irradiation units can span a triangle and,where a fourth irradiation unit is provided, a quadrilateral. Likewise,it can be provided that the irradiation system comprises a plurality ofgroups which each comprise a specific number of irradiation units whichdefine a corresponding polygon. These groups can be so arranged relativeto one another that a predetermined pattern of irradiation units isobtained overall. In addition or alternatively, the irradiation unitscan be arranged in rows, wherein immediately adjacent rows are offsetrelative to one another in at least two directions (for example along X-and Y-axes running orthogonally to one another of the irradiationplane).

The centers of the irradiation regions can be understood as meaning ageometric center or, in other words, a geometric midpoint. The shape ofthe irradiation regions can generally be arbitrary and have, forexample, a quadrilateral, pentagonal, hexagonal, heptagonal or octagonalshape. The center can be formed by the intersection of the diagonalsbetween opposite corner points of that shape. A circular shape of theirradiation regions is also conceivable. According to a variant, all theirradiation regions have the same shape, for example a quadrilateral orhexagonal shape, and/or have the same size.

In the case of a plurality of groups of irradiation units too, it can beprovided that the irradiation regions of in each case at least threeirradiation units coincide in a common overlap region. In addition,there can also be overlap regions in which the irradiation regions ofonly two irradiation units coincide. It can further be provided that theirradiation region of an individual irradiation unit has a plurality ofoverlap regions with adjacent irradiation units and in particular aplurality of overlap regions with two further irradiation units.Primarily, at least half or all of the overlap regions can be formed bynot more than three different irradiation regions, for example in orderto avoid imprecise transitions within the workpiece structuremanufactured in that region.

Preferably, the method further provides a step of selecting at least oneirradiation unit to be used for irradiating the overlap region. Inprinciple, all of the at least three irradiation units are available inthe overlap region for performing an irradiation of the portion of theraw material powder layer in that region. According to the presentfurther development, at least one, at least two or generally up to n-1irradiation units can be selected from the totality of the irradiationunits, where n indicates the total number of irradiation units. Inprinciple it is, however, also conceivable that, at least for theirradiation of selected raw material powder layers, all of theirradiation units are selected for irradiating the overlap region.

A further development provides that the selection step is carried outagain before the further workpiece layer is irradiated, that is to say,for example, before the further workpiece layer is irradiated accordingto method step c).

Accordingly, it can be provided that the step of selecting theirradiation units to be used for the overlap region is repeated layer bylayer. The selection of the irradiation units can generally be madeaccording to the contour, the irradiation pattern or othercharacteristics of the workpiece layer currently to be produced and canthus also be individually adapted layer by layer. In addition oralternatively, the selection can be made according to one of thecriteria discussed hereinbelow, wherein all the selection criteria canbe weighted relative to one another, prioritized and/or buildhierarchically on one another in order to select in a preferred mannerthe irradiation units to be used in the overlap region.

The method can further provide that the selection of the irradiationunits to be used for the overlap region differs between two successiveraw material powder layers. In other words, this variant provides thatthe groups of irradiation units defined by the selection differ from oneanother between two successive raw material powder layers, wherein thesegroups can also comprise only one irradiation unit. In other words,based on successive raw material powder layers, the irradiation unitsselected and thus usable can be changed layer by layer.

For example, a first and a second irradiation unit can be selected forthe irradiation of a first raw material powder layer in the overlapregion. For the irradiation of a following second raw material powderlayer in the overlap region there can then be selected, on the otherhand, only the first, only the second or only the third irradiation unitas well as, alternatively, the second and the third irradiation units orthe first and the third irradiation units. The first and the secondirradiation unit, on the other hand, cannot be used again forirradiating the overlap region of this further raw material powderlayer.

By selecting different usable groups of irradiation units for successiveraw material powder layers (i.e. by making different selections), theoverlap region is irradiated layer by layer by different irradiationunits. In other words, the usable irradiation units can be changedbefore each raw material powder layer to be irradiated, so thatindividual influences of individual irradiation units on the workpiecestructure become less noticeable at least in the overlap region. Thehomogeneity of the workpiece structure and the quality of the workpiececan thus be improved.

It will be noted that this can also be applied to a plurality of, forexample, 100 raw material powder layers, wherein before each irradiationof one of those raw material powder layers, a fresh selection and thus afresh change of the irradiation units which can be used in the overlapregion can take place. It will further be appreciated that it can alsobe provided according to the invention that such a change of theselected irradiation units is not carried out between each of the rawmaterial powder layers to be irradiated. Instead, this selection can,for example, also be kept constant over a predetermined number ofsuccessive raw material powder layers.

In general, it can be provided that the method is applied to at leasttwo successive raw material powder layers to be irradiated. The numberof successive raw material powder layers to be irradiated can likewisecomprise at least 10, at least 50, at least 200 or at least 500.Likewise, it can be provided that, in respect of an operation ofmanufacturing a single workpiece, a plurality of groups of successiveraw material powder layers to be irradiated are defined, within whichthe present method is applied, not, however, between those groups.Primarily, the present method can be applied to at least 20%, at least50%, at least 80% or about 100% of the raw material powder layers whichare to be irradiated within the context of an operation of manufacturingan individual workpiece.

A further development provides that a plurality of irradiation units isselected for the irradiation of the overlap region, in order toirradiate the overlap region in parallel or in succession. Byparallelizing the irradiation of the overlap region, the production timeof the corresponding workpiece layer can be reduced.

According to a further embodiment, the following step is carried out forselecting the irradiation units for the overlap region:

-   -   selecting irradiation units for the irradiation of the overlap        region in the irradiation regions of which the workpiece layer        to be produced also extends outside the overlap region.

In particular, only such irradiation units can be selected for theirradiation of the overlap region. In other words, it can be providedthat, for the irradiation of the overlap region, no irradiation unit isselected that is not used further outside the overlap region forproducing the current workpiece layer. To that end it can first bedetermined in a preceding step in which processing regions a workpiecelayer currently to be produced also extends outside the overlap region.A better transition can thus be achieved in the workpiece structurebetween the overlap region and the adjoining portions of the workpiecelayer, since the smallest possible number of irradiation units is usedtherefor. In this connection it can further be provided thatpredominantly or only those irradiation units that produce portions ofthe workpiece layer that directly adjoin the overlap region areselected. In other words, it can be provided that an evaluation iscarried out to determine the irradiation regions into which theworkpiece layer to be produced directly extends starting from theoverlap region. It is then possible to select predominantly or onlythose irradiation units which are associated with those irradiationregions. Consequently, it can also be provided, for the irradiation ofthe overlap region, not to select any irradiation units which produceportions of the workpiece layer to be produced at any point outside theoverlap region. Instead, irradiation units that operate in the immediatevicinity of or at the transition to the overlap region can be selected.

If the variant discussed above, according to which the selection ofirradiation units for irradiating the overlap region should wherepossible be changed layer by layer, is provided at the same time, aprioritization between those selection criteria can also be made. Forexample, it can be provided that a selection of possible irradiationunits is first made in consideration of the portions of the workpiecelayer that are to be produced outside the overlap region, whereupon itis then checked whether those irradiation units allow the irradiationunits which can be used in the overlap region to be changed layer bylayer. If that is not the case, the operation can, according to theprioritization, nevertheless be continued with the irradiation unitsfirst selected, or that selection is discarded and the irradiation unitsare selected solely to achieve the desired layer by layer change of theirradiation units used.

Alternatively, it can also be provided to select irradiation units forthe irradiation of the overlap region in whose irradiation regions theworkpiece layer to be produced does not extend outside the overlapregion. This permits an improved utilization level of the irradiationunits and/or a time saving in the production of an individual workpiecelayer, since the overlap region can be irradiated by irradiation unitswhich are otherwise not required. Outside the irradiation region, on theother hand, those irradiation units which are in any case required forproducing a current workpiece layer can be used, since the workpiecelayer to be produced also extends outside the overlap region in theirradiation regions thereof. Figuratively speaking, the irradiationunits which already perform irradiation outside the overlap region canthus be relieved, since other irradiation units, which otherwise wouldnot be required, are used within the overlap region. The portions of theworkpiece layer to be produced overall can thus be distributed moreevenly between the irradiation units. In particular, the manufacturingtime of an individual workpiece layer can thus be reduced, since ahigher degree of parallelization in the irradiation of the raw materialpowder layer can be achieved.

According to a further development it is provided that the definition ofthe irradiation regions is carried out in such a manner that thearrangement of the overlap region within the irradiation plane changesbetween two successive raw material powder layers. For example, theoverlap region can be arranged in a first position within theirradiation plane for irradiating a first raw material powder layer, andfor irradiating a second raw material powder layer it can be arranged ina second position, which is different from the first position.

In other words, it can be provided that the overlap region does notremain in a constant position or arrangement within the irradiationplane. Instead, it can be newly positioned for the irradiation of afollowing or even generally before each new raw material powder layer tobe irradiated. It can thus be achieved that the overlap region, relativeto the manufactured workpiece, does not maintain a locally constantposition but can change its position at least between selected workpiecelayers or in all the workpiece layers. Any inhomogeneities associatedwith the irradiation of the overlap region, such as, for example,imprecise transitions in the workpiece structure between the overlapregion and the adjoining irradiation regions, can thus be reduced and/ordistributed more evenly over the workpiece as a whole.

The irradiation regions can in this connection be redefined before or inparallel with the irradiation of a new raw material powder layer,whereby a new positioning of the overlap region can also be achieved.This can take place, for example, by suitably calculating a new positionand extent of the irradiation regions and/or by reading out suitable,previously stored positions from a memory.

Primarily, the overlap region can thus preferably be displaced, for eachlayer, within the irradiation plane in at least two directions which areat an angle to one another, for example along mutually orthogonal axes.These can be a conventional X- and Y-axis of the irradiation plane or ofthe carrier build area. The displacement can take place randomly oraccording to a predetermined pattern. For example, the overlap region,considered over a plurality of successive raw material powder layers,can be displaced in the manner of a spiral within the irradiation plane.

The method can further method comprise the following steps:

-   -   subdividing the overlap region into a plurality of partitioning        regions which are each associated with at least one of the        irradiation units; and    -   changing the partitioning region boundaries, so that the        partitioning regions differ from one another between two        successive raw material powder layers.

This further development can help to avoid fixed or locally constantinhomogeneities in the workpiece structure by varying the irradiationconditions within the overlap region. In addition or alternatively, theoverlap region itself can, however, also be variably positioned withinthe irradiation plane in the manner described above and/or the selectionof the usable irradiation units can purposively be varied.

The partitioning regions, similarly to the irradiation regions, theoverlap region and the irradiation plane, can define virtual regionswithin which the irradiation units can be used. When three irradiationunits are used, for example, an overlap region of triangular shape canin turn be subdivided into individual triangles which form correspondingpartitioning regions and are each associated with one of the irradiationunits. Likewise, when four irradiation units are used, a quadrilateraloverlap region can be defined, which can in turn be subdivided intoindividual quadrilaterals by corresponding partitioning regions. Theposition, size, number and/or shape of the partitioning regions canthereby purposively be varied between successive raw material powderlayers by changing the partitioning region boundaries.

Consequently, a portion of the overlap region that is associated witheach of the irradiation units can vary between the successive rawmaterial powder layers. As a result, the irradiation units can performdifferent irradiation operations in the overlap region, even if theworkpiece layer to be produced remains the same, since differentpartitioning regions are associated therewith layer by layer.

In general, the partitioning region boundaries can define predeterminedregions in which a transfer between the irradiation units immediatelytakes place. In other words, irradiation can be performed by a firstirradiation unit according to a predetermined irradiation vector oralong a workpiece contour that is to be produced unit a partitioningregion boundary is reached. When that boundary is crossed, theirradiation is continued by a second irradiation unit. However, it islikewise conceivable that the partitioning regions do not define anarrow region at which such a transfer immediately takes place. Instead,it can be provided, for example, that an irradiation unit continues anirradiation along a predetermined irradiation vector even beyond apartitioning region boundary, that is to say does not immediately ceaseirradiation on reaching the partitioning region. However, it can therebybe provided that the irradiation unit does not begin irradiation alongfurther vectors which, from the point of view of the irradiation unit,only begin after the partitioning region boundary. In other words, thepartitioning region boundary can define a region beyond which newirradiation operations cannot be begun by the irradiation units. This isrelevant in particular when irradiation is to be performed along aplurality of parallel irradiation vectors with predetermined lengths inorder to produce filled workpiece layers.

Further details of this procedure and the interaction of thepartitioning region boundaries with the chosen irradiation strategy areto be found in EP 2875897. Within the context of the present disclosure,explicit reference is made to the discussion of FIGS. 4 and 5 of EP2875897.

In this connection it can further be provided that the change of thepartitioning region boundaries comprises a displacement of anintersection point of the partitioning region boundaries. If, forexample, four irradiation units are used, each of which is associatedwith a quadrilateral partitioning region of the overlap region, thepartitioning region boundaries can intersect at a common point which,when the partitioning regions are of the same size, corresponds to ageometric midpoint of the overlap region. The displacement of such anintersection point can generally take place within the irradiation planeand preferably in at least one of two directions extending at an angleto one another. Analogously to the displacement of the overlap region asa whole, the directions can be mutually orthogonal axes, for example theX- and Y-axes of the irradiation plane or of the carrier build area. Itwill be appreciated that, when the intersection point is displaced, thepartitioning region boundaries can automatically be adjusted and thesize ratios of the partitioning regions correspondingly changeautomatically.

The displacement of the intersection point can take place randomly oraccording to a predetermined pattern, wherein a spiral-shapeddisplacement over successive raw material powder layers may again bementioned as being a suitable example.

A further development provides that the irradiation system comprises atleast one group of at least three irradiation units, and the methodfurther comprises the following steps:

-   -   arranging the irradiation units in such a manner that the        irradiation units together span a polygon; and    -   defining the irradiation regions for each irradiation unit in        such a manner that the common overlap region is arranged at        least in part within the polygon.

As discussed above, in the case of a group of, for example, threeirradiation units, a common triangle can be spanned. The overlap regioncan be positioned at least in part therein (for example in the middle).Each irradiation unit can thereby have a rectangular or squareirradiation region. As a further example there may be mentioned a groupof three irradiation units which each have a hexagonal irradiationregion. In general, each irradiation unit of such a group can have anirradiation region which also overlaps with at least one irradiationregion of a further irradiation unit from an adjacent group.

The invention relates further to a device for the layer by layermanufacture of three-dimensional workpieces, comprising:

-   -   an irradiation system having at least three irradiation units;    -   a carrier, which is adapted to receive a raw material powder        layer which can be irradiated by the irradiation system to        produce a workpiece layer;    -   a control unit, which is adapted to define an irradiation region        for each of the irradiation units, wherein the irradiation        regions each comprise a portion of an irradiation plane which        extends parallel to the carrier, and wherein the control unit is        further adapted to define the irradiation regions in such a        manner that they overlap in a common overlap region;        wherein the control unit is further adapted to control the        device in such a manner that raw material powder layers arranged        in succession on the carrier can be irradiated by the        irradiation system to produce successive workpiece layers.

The device can generally comprise any further features and components inorder to be able to carry out all the steps mentioned above and toachieve all the effects mentioned above. In particular, the control unitcan be configured to perform all variants in respect of the selection ofthe irradiation units to be used in the overlap region, the variation ofthe position of the overlap region in the irradiation plane, and thedefinition and/or changing of any partitioning regions.

According to a further variant, the device comprises at least fourirradiation units and the irradiation regions are so defined that allthe irradiation regions of the irradiation units overlap in a commonoverlap region. This lies preferably at least in part within aquadrilateral spanned by the irradiation unit.

The invention will be explained hereinbelow with reference to theaccompanying figures, in which:

FIG. 1 : is a view of a device according to the invention which carriesout a method according to the invention;

FIG. 2 : is a representation of the irradiation regions of the device ofFIG. 1 ;

FIG. 3 : is a representation of possible partitioning regions of thedevice of FIG. 1 ; and

FIGS. 4, 5 : show possible arrangements of the irradiation units in adevice of FIG. 1 .

FIG. 1 shows a device 10 which is configured to carry out a methodaccording to the invention for the additive manufacture ofthree-dimensional workpieces from a metallic powder bed. More precisely,the method relates to a manufacturing process in the manner of so-calledselective laser melting (SLM). The device 10 comprises a process chamber12. The process chamber 12 can be sealed with respect to the surroundingatmosphere, so that an inert gas atmosphere can be established therein.A powder application device 14, which is arranged in the process chamber12, applies raw material powder layers to a carrier 16. As is shown inFIG. 1 by an arrow A, the carrier 16 is adapted to be displaceable in avertical direction. The carrier can thus be lowered in the verticaldirection as the build height of the workpiece increases as it is builtup layer by layer from the selectively solidified raw material powderlayers.

The device 10 further comprises an irradiation system 20 for selectivelyand location-specifically directing a plurality of laser beams 24 a,bonto the raw material powder layers on the carrier 16. More precisely,the raw material powder material can be exposed to radiation by means ofthe irradiation system 20 in accordance with a geometry of a workpiecelayer that is to be produced, and thus locally melted and solidified.

The irradiation system comprises four irradiation units 22 a-d, of whichonly the front two irradiation units 22 a-b are visible in FIG. 1 . Thefurther irradiation units 22 c-d, on the other hand, are displaced intothe plane of the drawing and thus arranged behind the irradiation units22 a-b visible in FIG. 1 .

Each of the irradiation units 22 a-d is coupled to a common laser beamsource. The laser beam emitted by the laser beam source can be splitand/or deflected by suitable means, such as, for example, beam splittersand/or mirrors, in order to guide the laser beam to the individualirradiation units 22 a-d. Alternatively, it would be conceivable toallocate each of the irradiation units 22 a-d its own laser beam source.A suitable laser beam source can be provided, for example, in the formof a diode-pumped ytterbium fiber laser having a wavelength ofapproximately from 1070 to 1080 nm.

Each of the irradiation units 22 a-d further comprises a processing beamoptics, in order to interact with the laser beam provided. Theprocessing beam optics each comprise a deflection device in the form ofa scanner unit, which is able flexibly to position the focus point ofthe laser beam 24 a,b emitted in the direction of the carrier 16 withinan irradiation plane 28 extending parallel to the carrier 16.

The irradiation plane 28 represents a virtual plane which contains a rawmaterial powder layer which is arranged uppermost on the carrier 16 andis currently to be irradiated to produce a workpiece layer. The positionof the irradiation plane 28 thus changes relative to the carrier 16 asthe number of applied and irradiation raw material powder layersincreases. By lowering the carrier 16, however, it can also be providedthat the position of the irradiation plane 28 relative to theirradiation units 22 a-d does not change, since it is always arrangedconstantly inside the process chamber 12.

The irradiation of the raw material powder layers by the irradiationsystem 20 is controlled by a control unit 26. The control unit isfurther configured to define for each of the irradiation units 22 a-d alikewise virtual irradiation region 18 a-d which each extend in theirradiation plane 28 and comprise a predetermined portion thereof. Inthe representation of FIG. 1 , again only the irradiation regions 18 a-bof the irradiation units 22 a-b visible therein are shown.

FIG. 2 shows a plan view of the carrier 16 and the irradiation plane 28from the point of view of the irradiation system 20. It will be seenthat the irradiation plane 28 is square in shape and accordinglycomprises four quadrants I-IV of equal size. One of the irradiationunits 22 a-d is arranged approximately in the center of each of thosequadrants I-IV. The control unit 26 defines an irradiation region 30 a-dfor each of the irradiation units 22 a-d. In the case shown, theirradiation regions 30 a-d for each of the irradiation units 22 a-d arechosen to be of equal size and rectangular. Furthermore, they are sodefined that the irradiation units 22 a-d are arranged slightlyeccentrically within the irradiation regions 30 a-d.

The outline or, in other words, the region boundary, of the irradiationregion 30 a is picked out in FIG. 2 by a broken line. The same is truefor the outline of the irradiation region 30 d, which is depicted by adot-and-dash line. The outlines of the further irradiation regions 30b,c are in principle chosen to be of similar type. Consequently, it willbe seen that the irradiation regions 30 a-d overlap several times,wherein overall a cross-shaped overlap zone 32 is defined within theirradiation plane 28.

In its center, the overlap zone 32 has a common overlap region 34, inwhich all the irradiation regions 30 a-d coincide and overlap. Startingfrom this overlap region 34, which in the present case is square,further secondary overlap regions 36, in which in each case only two ofthe irradiation regions 30 a-d overlap, extend in a cross shape.

In summary, it will thus be seen that the irradiation units 22 a-d areso arranged that they together span a polygon in the form of arectangle, and that their irradiation regions 30 a-d are further sodefined that the common overlap region 34 is arranged centrally withinthe rectangle.

In FIG. 2 , an outline of a workpiece layer 38 to be produced is alsoshown. In known manner, it is provided that the outer contour thereof isproduced by location-specific irradiation and solidification of thecurrently uppermost raw material powder layer. In addition oralternatively, it can be provided that the workpiece cross-sectionalarea framed by the outline is formed substantially completely solidifiedand thus filled or, in other words, solid. This can take place by meansof known irradiation patterns comprising, for example, a plurality ofscan vectors running parallel to one another.

Primarily, it will be seen from FIG. 2 that the workpiece layer 38 to beproduced has different portions with which it extends into theindividual irradiation regions 30 a-d, but also into the overlap region34 and the secondary overlap regions 36. In order to produce theworkpiece layer, the irradiation units 20 a-d must thus be controlled ina coordinated manner by the control unit 26 in order that they are eachable to produce a portion of the workpiece layer 38 that is assigned tothem.

In those cases in which a relevant portion of the workpiece layer 38 tobe produced extends solely in one of the irradiation regions 30 a-d andoutside the overlap zone 32, that portion can be directly solidified bythe associated irradiation unit 22 a-d. For those portions of theworkpiece layer 28 that extend within the overlap zone 32, on the otherhand, the control unit 26, which carries out the method according to theinvention, provides that the irradiation units 20 a-d actually used forthe irradiation are purposively selected.

In FIG. 2 there are shown, for example, a plurality of double-headedarrows 1-4 which each extend between two of the irradiation regions 30a-d and pass through one of the secondary overlap regions 36. If, forthe production of a desired workpiece layer, a laser beam 24 a-b is tobe guided along one of those double-headed arrows 1-4, the control unit26 decides which of the irradiation units 22 a-d within the commonsecondary overlap region 36 should perform the irradiation of the rawmaterial powder layer. In addition or alternatively, however, it canalso be provided that both of the irradiation units 22 a-d that areassociated with a common secondary overlap region 36 are selected forthis irradiation.

In the case of the double-headed arrow 1, this means that, in the caseof an irradiation movement from bottom to top in FIG. 2 , irradiation isfirst performed by the irradiation unit 22 b, until the secondaryoverlap region 36 between the irradiation regions 30 b and 30 d isreached. From that point onwards, the control unit 26 can, for example,specify that the irradiation unit 22 b continues the irradiation untilit reaches the upper boundary of the secondary overlap region 36 in FIG.2 . The further irradiation along the double-headed arrow 1 must then betaken over by the irradiation unit 22 d.

However, two further double-headed arrows 5-6 are also shown in FIG. 2 ,which arrows extend diagonally within the irradiation plane 28 and inparticular through the common overlap region 34. Since all theirradiation regions 30 a-d overlap within that overlap region 34, thecontrol unit can choose in that region between all the irradiation units22 a-d in order to irradiate the portion of the raw material powderlayer enclosed thereby.

In relation to the double-headed arrow 5, and when considered frombottom left to top right in FIG. 2 , this means that irradiation firsttakes place by means of the irradiation unit 22 a, until the commonoverlap region 34 is reached. There, the control unit 26 can thenspecify which of the irradiation units 22 a-d is to be selected for theirradiation of the raw material powder layer in that region, or whethereven a plurality or all of the irradiation units 22 a-d should worktogether for that purpose. After crossing the common overlap region 34,the irradiation along arrow 5 is again continued with the upper rightirradiation unit 22 d in FIG. 2 .

When selecting the irradiation units 22 a-d for irradiating the overlapregion 34, the control unit 26 can consider only those irradiation units22 a-d which are also used outside the overlap region for carrying outthe desired irradiation. The further irradiation units 22 b,c, which arenot used for irradiation outside the common overlap region 34, on theother hand, can deliberately not be selected in order to minimize therisk of imprecise transitions within the workpiece structure due tofrequent changing of the irradiation units 22 a-d.

It is an aim of the exemplary embodiment shown to make use of themultiple overlaps of the irradiation regions 30 a-d and the describedselection possibilities between the irradiation units 22 a-d to be used,in such a manner that the structure of the manufactured workpiece is ashomogeneous as possible. The inventors have recognized that animprovement in homogeneity can be achieved, for example, if theirradiation conditions are chosen to be as variable as possible in ordernot to produce the same inaccuracies at the same position in eachworkpiece layer.

According to the present exemplary embodiment, this can be achieved inthat, for each individual raw material powder layer to be irradiated, itis selected which of the irradiation units 22 a-d are actually used inthe common overlap region 34 and/or the secondary overlap regions 36.Furthermore, it is ensured that this selection differs in successive rawmaterial powder layers. Owing to the constantly changing selection ofirradiation units 22 a-d, the irradiation conditions within the overlapzone 32 can thus be changed layer by layer.

It can likewise be provided according to the present exemplaryembodiment that, by redefining at least some of the irradiation regions30 a-d layer by layer, a position of the common overlap region 34 withinthe irradiation plane 28 is changed layer by layer. The overlap region34, and in particular a geometric midpoint thereof, is thereby displacedwithin the irradiation plane 28. The overlap region 34 is therebydisplaced along at least one of the X-Y-axes of the irradiation plane 28running orthogonally to one another, before irradiation of a new rawmaterial powder layer, either randomly or according to a predeterminedpattern.

There comes into consideration as a predetermined pattern a spiral,wherein the overlap region 34 shown in FIG. 2 is arranged at the centerof such a spiral. It is likewise conceivable to displace the overlapregion in the manner of a so-called knight's move. Further suitablepatterns can be a so-called “random chessboard”, which also includes arandom movement component, or a movement in accordance with a “maximumspacing”.

FIG. 3 shows a further variant for irradiating the raw material powderlayer, which variant can be carried out with the present embodiment.There will again be seen the irradiation plane 28 and the cross-shapedoverlap zone 32 arranged therein. With the exception of the subdivisionof the overlap zone described hereinbelow, this example is analogous tothat of FIG. 2 . Therefore, for reasons of clarity, not all thereference numerals have been entered in FIG. 3 .

FIG. 3 shows various possibilities of how the overlap zone 32 can besubdivided in different ways by varying partitioning region boundariesbetween successive raw material powder layers to be irradiated. Acurrent position of the partitioning region boundaries is shown in FIG.3 by solid and broken lines.

FIG. 3 shows by dotted lines further variants of the choice of thepartitioning region boundaries. Overall, it will be seen that theoverlap zone 32 can be subdivided into different partitioning zonesaccording to the choice of partitioning region boundaries, whichpartitioning zones can be composed, for example, of the portions PS1x-PS4 x, PS1 y-PS4 y shown in FIG. 3 . These partitioning regions canagain each be associated with one of the irradiation units 22 a-d.

The choice of suitable partitioning region boundaries and associatedpartitioning regions of the overlap zone 32 can take place in particularwith regard to the common overlap region 34. There it will be seen thatthe partitioning region boundaries intersect at a common point P. Thecommon overlap region 34 is accordingly likewise divided into fourportions of different sizes, each of which forms a partitioning regionT1-4 of the common overlap zone 34. Each of those partitioning regionsT1-4 is associated with one of the irradiation units 22 a-d, wherein theupper left irradiation unit 22 c in FIG. 3 is associated with thelargest partitioning region T1 and the lower right irradiation unit 22 bis associated with the smallest partitioning region T3.

As discussed above, a transfer between the irradiation units 22 a-d cantake place immediately at the partitioning region boundaries in order toproduce a common workpiece layer (that is to say, irradiation isimmediately continued by an irradiation unit 22 a-d that is associatedwith an adjacent partitioning region). In addition or alternatively, thepartitioning region boundaries can also merely define a general regionwhich can also temporarily be crossed, for example in the case ofirradiation along a predetermined vector by the irradiation units 22a-d. Irradiation along a new irradiation vector which from the point ofview of the irradiation unit 22 a-d in question only begins after thepartitioning region boundary cannot be made possible, however.

In order to vary the irradiation conditions between successive rawmaterial powder layers, the embodiment shown provides the possibility ofvarying the position of the intersection point P of the partitioningregion boundaries within the common overlap region 34. Concretely, theintersection point P can be displaced along at least one of theX-Y-axes. Analogously to the displacement, discussed above, of thecommon overlap region 34 as a whole, the intersection point P can bedisplaced randomly or according to a predetermined pattern. As aconsequence of the displacement of the intersection point P, the sizesof the partitioning regions T1-4 also change.

Consequently, the same portion of the common overlap region 34 can beirradiated by different irradiation units 22 a-d depending on a positionof the intersection point P and considered over a plurality ofsuccessive raw material powder layers, namely depending on thepartitioning region T1-T4 in which the relevant portion is currentlycontained.

For the sake of completeness, the possibility of subdividing the uppersecondary overlap region 36 shown in FIG. 3 will be discussedhereinbelow. In this case there will be seen four possible subdivisionsby the choice of corresponding secondary partitioning regions N1, N2,each of which is composed of the portions PS1 x-PS4 x. Owing to thecurrently chosen partitioning region boundaries, a comparatively smallportion PS4 x is associated with the upper right irradiation unit 22 din FIG. 3 . A significantly larger portion of this secondary overlapregion 36, comprising the further portions PS1 x-PS3 x, on the otherhand, is associated with the upper left irradiation unit 22 c.

As explained, the partitioning region boundaries can be changed betweensuccessive raw material powder layers by means of the control unit 26.This can take place in particular in that the secondary partitioningregions N1, N2 defined by the portions PS1 x-PS4 x differ from oneanother between the successive raw material powder layers. If, forexample, in the variant according to FIG. 3 the irradiation of thecurrent raw material powder layer is complete, the control unit 26 candisplace the partitioning region boundaries represented by broken linesso that the upper secondary overlap region 36 is divided in the middle.Consequently, a secondary partitioning region N1 comprising the portionsPS3 x-PS4 x would be associated with the irradiation unit 22 d, and asecondary partitioning unit N2 comprising the portions PS1 x-PS2 x wouldbe associated with the irradiation unit 22 c.

It will be appreciated that this can also be carried out for all furthersecondary overlap regions 36. In the exemplary embodiment shown,however, all the subdivisions of the secondary overlap regions 36 and ofthe common overlap region 34 are varied at the same time, namely by theabove-described displacement of the intersection point P within thecommon overlap region 34.

In summary, several possibilities are thus provided which utilize thepresence of at least three irradiation units 22 a-d and of an overlapregion 34 formed thereby in order to improve the homogeneity of amanufactured workpiece structure. These possibilities concern thedisplacement of the overlap region 34 and the variable selection of theirradiation units 22 a-d according to FIG. 2 and the variablesubdivision of the overlap zone 32 by individual partitioning regionsT1-T4 according to FIG. 3 . The device 10 can in principle be configuredto perform all of these possibilities. Which of these possibilities isapplied to individual or also a plurality of successive raw materialpowder layers can be determined beforehand for the entire workpiece thatis to be manufactured or also individually for each workpiece layer thatis to be produced.

FIGS. 4 and 5 show further possibilities for the arrangement of aplurality of irradiation units, which are shown in the form of crossesand are always provided with the same reference numeral 50. For reasonsof clarity, however, not all the irradiation units have been providedwith that reference numeral. The views of FIGS. 4 and 5 , analogously toFIGS. 2 and 3 , likewise show a plan view of an irradiation plane 28.The arrangements of the irradiation units 50 shown in FIGS. 4 and 5 canin principle be used in the device 10 discussed above. Therefore, in thefollowing, the same reference numerals will be used for features of thesame type or having the same effect.

In FIG. 4 it will be seen that a total of nine irradiation units 50 areprovided, which are offset relative to one another within theirradiation plane 28 along the Y-X-axes. Concretely, three irradiationunits 50 arranged one behind the other in the Y direction are shown,wherein a total of three of these rows are provided and spaced apartfrom one another along the X-axis. A middle row is offset downwardsrelative to the outside rows when viewed in the Y direction. Overall,this has the result that a group of three irradiation units 50 is formedin each case, the square irradiation regions 52 of which units overlapin a common overlap region 34. For reasons of clarity, not all theirradiation and overlap regions 34, 52 in FIGS. 4 and 5 are providedwith a corresponding reference numeral.

The spanning of a triangle is shown more precisely in FIG. 4 for twoselected groups. It will be seen that the irradiation units 50 are ineach case arranged in the middle of their square overlap regions 52. Theirradiation units 50 within a group thereby span a schematicallyindicated virtual triangle, in which the common overlap region 34 isalmost completely arranged. Again, there will also be seen a pluralityof secondary overlap regions 36, in which only the irradiation regions52 of two irradiation units 50 overlap. It will further be seen thateach irradiation unit 50 interacts with further irradiation units 50outside an individual group spanning a triangle and also overlaps withthe irradiation regions 52 thereof. In other words, one irradiation unit50 can be associated with a plurality of groups of irradiation units 50with which it forms a common overlap region 34. This concerns, forexample, the irradiation unit 50 marked by the arrow Z in FIG. 4 , whichis to be associated with both of the triangle-shaped groups shown inFIG. 4 .

Consequently, the irradiation units 50 in FIG. 4 are so arrangedrelative to one another that their irradiation regions 52 form at leasttwo common overlap regions 34 with in each case two further irradiationunits 50.

It will be appreciated that, in the case of FIG. 4 too, all of theabove-mentioned possibilities for varying the irradiation conditions canbe applied, for example in the form of a variable selection ofirradiation units 50 to be used in the overlap regions 34 or a variabledisplacement of the positions of the overlap regions 34 within theirradiation plane 28.

The same also applies to the variant according to FIG. 5 , in which atotal of fourteen irradiation units 50 are arranged in mutually offsetrows. The irradiation units 50 each have hexagonal or, in other words, ahoneycomb-shaped irradiation region 52. For reasons of clarity, againnot all of the described features are provided with a correspondingreference numeral.

The irradiation units 50 are again so arranged that groups of threeirradiation units 50 are formed, which together span a triangle whichencloses a common overlap region 34. It will additionally again be seenthat each irradiation unit 50 interacts with a plurality of adjacentirradiation units 50 and thus also defines a plurality of common overlapregions 34 and/or secondary overlap regions 36. Both in FIG. 4 and inFIG. 5 , however, no overlap regions 34 are formed by more than threedifferent irradiation regions 52, which as before permits precisetransitions in the workpiece structure with nevertheless variableirradiation possibilities.

The invention claimed is:
 1. A method for controlling an irradiationsystem, wherein the irradiation system is used in a device for theadditive manufacture of three-dimensional workpieces, the irradiationsystem comprising at least three irradiation units, wherein the methodcomprises the following steps: defining an irradiation region for eachof the irradiation units, wherein the irradiation regions each comprisea portion of an irradiation plane which extends parallel to a carrier ofthe device and wherein the irradiation regions each comprise at least aportion of a raw material powder layer arranged on the carrier toproduce a workpiece layer, and wherein the irradiation regions are sodefined that they overlap in a common overlap region; subdividing theoverlap region into a plurality of partitioning regions, each of whichis associated with at least one of the irradiation units, whereinpartitioning region boundaries of the partitioning regions intersect ata common intersection point; irradiating the raw material powder layerarranged on the carrier using the defined irradiation regions to producea workpiece laver; arranging a further raw material powder layer on thealready irradiated raw material powder layer to produce a furtherworkpiece layer; and changing the partitioning region boundaries so thatthe partitioning regions differ from one another between two successiveraw material powder layers, wherein a position of the commonintersection point is varied.
 2. The method as claimed in claim 1,wherein the proportions of the irradiation regions relative to a totalarea of the irradiation plane are each greater than 0% and less than100%, and/or wherein the proportion of the overlap region relative to atotal area of the irradiation plane is greater than 0% and less than100%.
 3. The method as claimed in claim 1, wherein the irradiation unitsand/or centers of the irradiation regions span a polygon.
 4. The methodas claimed in claim 1, further comprising the step of: selecting atleast one irradiation unit to be used for irradiation of the overlapregion.
 5. The method as claimed in claim 4, wherein the selection stepis carried out again before the further workpiece layer is irradiated.6. The method as claimed in claim 4, wherein the selection of the atleast one irradiation unit to be used for the overlap region differsbetween two successive raw material powder layers.
 7. The method asclaimed in claim 4, wherein a plurality of irradiation units is selectedfor the irradiation of the overlap region, in order to irradiate theoverlap region by the plurality of irradiation units in parallel or insuccession.
 8. The method as claimed in claim 4, wherein, for selectingthe at least one irradiation unit for the overlap region, the followingstep is carried out: selecting at least one irradiation unit for theirradiation of the overlap region in the irradiation regions of whichthe workpiece layer to be produced also extends outside the overlapregion; or selecting at least one irradiation unit for the irradiationof the overlap region in the irradiation regions of which the workpiecelayer to be produced does not extend outside the overlap region.
 9. Themethod as claimed in claim 1, wherein the defining of the irradiationregions is carried out in such a manner that the arrangement of theoverlap region within the irradiation plane changes between twosuccessive raw material powder layers.
 10. The method as claimed inclaim 1, wherein the variation of the intersection point takes placerandomly or according to a predetermined pattern.
 11. The method asclaimed in claim 1, wherein the irradiation system comprises at leastone group of at least three irradiation units, comprising the steps of:arranging the irradiation units in such a manner that the irradiationunits together span a polygon; and defining the irradiation region foreach irradiation unit in such a manner that the common overlap region isarranged at least in part within the polygon.
 12. The method of claim 1,wherein the plurality of partitioning regions fill the entirety of theoverlap region.
 13. The method of claim 1, wherein subdividing theoverlap region comprises dividing the overlap region into the pluralityof partitioning regions such that a union of the plurality ofpartitioning regions equals the overlap region.
 14. The method of claim1, wherein changing the partitioning region boundaries compriseschanging the partitioning region boundaries so that each of theplurality of partitioning regions differs in size between two successiveraw material powder layers.
 15. A device for the layer by layermanufacture of three-dimensional workpieces, comprising: an irradiationsystem having at least three irradiation units; a carrier which isadapted to receive a raw material powder layer which is irradiatable bythe irradiation system to produce a workpiece layer; a control unitwhich is adapted to define an irradiation region for each of theirradiation units, wherein the irradiation regions each comprise aportion of an irradiation plane which extends parallel to the carrier,and wherein the control unit is further adapted to define theirradiation regions in such a manner that they overlap in a commonoverlap region; wherein the control unit is further adapted to controlthe device in such a manner that the overlap region is subdivided into aplurality of partitioning regions, each of which is associated with atleast one of the irradiation units, wherein partitioning regionboundaries of the partitioning regions intersect at a commonintersection point, and the partitioning region boundaries are changedso that the partitioning regions differ from one another between twosuccessive raw material powder layers, wherein a position of the commonintersection point is varied; and wherein the control unit is furtheradapted to control the device in such a manner that raw material powderlayers arranged in succession on the carrier are irradiatable using thedefined irradiation regions to produce successive workpiece layers. 16.The device of claim 15, wherein the plurality of partitioning regionsfill the entirety of the overlap region.
 17. The device of claim 15,wherein subdividing the overlap region comprises dividing the overlapregion into the plurality of partitioning regions such that a union ofthe plurality of partitioning regions equals the overlap region.
 18. Thedevice of claim 15, wherein changing the partitioning region boundariescomprises changing the partitioning region boundaries so that each ofthe plurality of partitioning regions differs in size between twosuccessive raw material powder layers.